The present invention relates to a roll control system for a motor vehicle.
GB-A-2230237 discloses a roll control system comprising a torsion bar, a first arm fixedly connected to one end of the torsion bar, and a second arm rotatably connected to the other end of the torsion bar by way of a rotary actuator. The rotary actuator is operable to effect relative angular movement between the second arm and the said other end of the torsion bar. This arrangement is such that the actuator has to generate a large amount of force in order to provide the required roll control.
GB-A-2284184 describes a roll control system in which a hydraulic cylinder is used to prevent or allow rotation of an arm attached to a torsion bar between the torsion bar and an axle of a wheel. This arrangement provides a limited amount of roll control.
EP-A-0783986 describes an arrangement which is similar in layout to GB-A-2284184 but in which the hydraulic actuators are powered to provided active roll control for the vehicle. EP-A-0512358 describes a twin-axle roll control system which makes use of an attitude sensor for controlling roll.
The vehicle roll control system of this invention comprises a torsion bar, a first arm attached to the torsion bar at one end of the first arm and connectable to one of the axles at the other end of the first arm, a hydraulic actuator attached to the torsion bar, and control means connected to the hydraulic actuator and controlling the operation thereof on detection of a predetermined vehicle condition. The hydraulic actuator comprises a housing, a piston making a sealing sliding fit inside the housing to define a first fluid chamber and a second fluid chamber, and a piston rod connected to the piston and extending through the second fluid chamber and out of the housing. The control means acts on detection of the predetermined vehicle condition alternatively (1) to apply substantially the same fluid pressure to the first and second fluid chambers when the piston tends to move in a first direction to extend the hydraulic actuator, or (2) to apply a fluid pressure to the second fluid chamber above the fluid pressure in the first fluid chamber when the piston tends to move in a second direction to compress the hydraulic actuator. The control means comprises a first directional valve and a second directional valve, with each directional valve being capable of moving between first and second positions so as to tend to move the piston in the first direction or to tend to move the piston in the second direction. The system provides active roll control with reduced hydraulic fluid flow which reduces the risk of cavitation in the fluid, and/or reduces the difference between response times during extension and compression of the hydraulic actuators.